Catalyst systems for the one step gas phase production of acetic acid from ethylene and methods of making and using the same

ABSTRACT

A mixed metal oxide catalytic system comprising MoVNbPd or MoLaVPd providing higher selectivity and space time yield of acetic acid in the low temperature single stage oxidation of ethylene with molecular oxygen-containing gas and steam with very minimum or without the production of side products such as acetaldehyde, and methods of using the same.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 08/997,913filed Dec. 24, 1997, and U.S. application Ser. No. 09/107,115 filedconcurrently herewith, by Karim et al., entitled "Catalysts for GasPhase Production of Acetic Acid from Ethane, Processes of Making theSame and Methods of Using Same", herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improved catalytic systems, including MoVNbPd,MoVLaPd and combinations thereof, and to improved catalytic processesfor the low temperature selective oxygenation of ethylene to aceticacid. More specifically, the invention relates to a single stagecatalytic process using novel catalysts for providing high ethyleneconversions and acetic acid yields.

2. Description of the Related Art

Several publications are referenced in this application. Thesereferences describe the state of the art to which this inventionpertains, and are incorporated herein by reference.

Acetic acid is generally produced by methanol carbonylation using anexpensive rhodium catalyst in a liquid phase homogeneous reaction. Thismethod requires complicated procedures for the recovery of the catalystand the isolation of the products. Moreover, the presence of iodine atppm levels in the final product has a negative impact on the usage ofthe acetic acid produced by the method.

Acetic acid is also produced by a two stage acetaldehyde process usingmanganese catalysts. Such processes are disclosed in U.S. Pat. Nos.3,131,223; 3,057,915; 3,301,905; and 3,240,805. The first stage of thisprocess involves the production of acetaldehyde from ethylene. Theeconomics of the process is not favored due to the costs arising fromthe two stages. Furthermore, these processes produce a large amount ofacetaldehyde as a by-product. In addition, a large amount of ethylenemay be lost by complete oxidation into carbon dioxide.

More recently, Showa Denko [EP 0 62 0205 A1] relates to a catalyticprocess for converting ethylene to acetic acid using catalystscontaining heteropoly acids of phosphorus, silicon, boron, aluminum,germanium, titanium, zirconium, cerium, cobalt, chromium and metalpalladium with at least one element selected from groups XI, XIV, XV,and XVI of the periodic table. The single pass conversion of ethylenewas reported to be very low over these heteropoly catalysts and producesa significant amount of acetaldehyde, which can have a great impact onthe separation cost. The catalytic systems used in the present inventionare different from the Showa Denko catalysts.

EP A 0 29 4845 relates to a process for the higher selective productionof acetic acid by the oxidation of ethane or ethylene with oxygen incontact with a physical mixture of at least two catalyst systemsconsisting of (A) a catalyst for oxydehydrogenation of ethane toethylene and (B) a catalyst for hydration/oxidation of ethylene. Theethane oxydehydrogenation catalyst is represented by the formula Mo_(x)V_(y) Z_(z), wherein Z can be one or more of the metals Nb, Sb, Ta, Ca,Sr, Ti, W, Li, Na, Be, Mg, Zn, Cd, Hg, Sc, Fe and Ni. The catalyst forhydration/oxidation is selected from a molecular sieve catalyst, apalladium-containing oxide catalyst, tungsten-phosphorus oxide catalyst,or tin or molybdenum containing oxide catalyst. EP A 0 29 4845 employsthe catalyst prepared by the physical mixing of the two types ofcatalysts.

Japanese Patent No. 46-6763 relates to the catalytic oxidation ofethylene to acetic acid using specific catalysts disclosed in theexamples containing the following combination of metal atoms: V-Pd-Sb,V-Rh-Sb, V-Pd-P, V-Rh-P, V-Rh-As, V-Pd-As, Mo-Pd-Sb, Mo-Rh-Sb, Mo-Rh-As,and Mo-P-W-Pd-Rh-Sb.

Japanese Patent No. 54-57488 relates to the use of NaPdH₂ -PMoVcatalysts for the oxidation of ethylene to acetic acid.

Syoji Tan et al. [J. Catal., vol. 17, pp. 132-142, 1970] reported thatolefins oxidize to ketones over the binary catalyst systems Co₃ O₄ -MoO₃and SnO₂ -MoO₃. The article discloses the formation of acetic acid as aby-product together with other compounds and product of specificallyethylene was only carbon dioxide.

Thus, none of the prior art discloses or suggests the advantages of thecatalytic system disclosed in present invention for the selectiveproduction of acetic acid from ethylene using a catalyst which is a dualfunction catalyst and is designed in such way that it enhances theactivation function as well as the selectivity to the desired productacetic acid.

OBJECTS OF THE INVENTION

It is an object of the invention to overcome the above-identifieddeficiencies.

It is another object of the invention to provide improved catalystsystems for the production of acetic acid.

It is yet another object of the invention to provide an improved methodof making acetic acid with enhanced selectivity and yield of the desiredproduct acetic acid.

It is a still further object of the invention to provide a method ofmaking improved catalysts for the production of acetic acid.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description.

SUMMARY OF THE INVENTION

The present invention relates to the selective oxidation of ethylenewith molecular oxygen to acetic acid in a gas phase reaction atrelatively high levels of conversion, selectivity and productivity attemperatures ranging from 150° C. to 450° C. and at pressures of 1-50bar. This is achieved by using a mixed metal oxides including MoVNbPd orMoVLaPd oxide catalysts, supported or unsupported, such as thosedisclosed in related U.S. application Ser. No. 08/997,913 filed Dec. 24,1997 and U.S. application Ser. No. 09/107,115, filed concurrentlyherewith.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For oxidation catalysts, the selectivity behavior to desired partialoxidation products depends on the types of active centers in thecatalysts in addition to other physical reaction parameters, such as (a)hydrocarbon to oxygen ratio, (b) pressure, (c) reaction temperature, and(d) contact time.

Generally, it is well known that selectivity to mild oxygenated productssuch as acetic acid increases as reaction temperature decreases, whereasyield is decreased on account of total conversion. Active sites involvedin the reaction play a key role in the direction of the reactions.Furthermore, the selectivity for the partial oxidation products dependson the reactivity of lattice oxygen to form C--O bonds with the adsorbedhydrocarbon. For example, alkenes are more reactive and adsorbpreferentially as compared to alkanes over metal oxide/acidic catalysts.Mixed metal oxide phases of MoV are known to be responsible for theactivation of hydrocarbon and the activity of the catalyst depends onthe relative number of V⁺⁴ and V⁺⁵ over the surface of the catalyst.Moreover, palladium is known as a total oxidation metal, as well as ametal that helps to facilitate the oxygenation of alkene. An optimumamount of Pd with a high degree of dispersion of metal over mixed metaloxide catalyst results in a high selectivity to acetic acid.

Furthermore, it has been discovered that the addition of water as aco-feed plays an important role as a reaction diluent and as a heatmoderator for the reaction and also acts as a desorption accelerator ofthe reaction product in the vapor phase oxidation reaction or maskingthe sites responsible for the total oxidation resulting in an increasedyield of acetic acid.

In carrying out the partial oxidation of ethylene process, the reactionmixture preferably contains one mole of ethylene, 0.01 to 2.0 moles ofmolecular oxygen (either as pure oxygen or in the form of air), and zeroto 5.0 moles of water in the form of steam. Other gases may be used asreaction diluents or heat moderators such as helium, nitrogen, andcarbon dioxide.

The gaseous components of the reaction mixture preferably includeethylene, oxygen and a diluent, and these components may be uniformlyadmixed prior to being introduced into the reaction zone. The componentsmay also be preheated, individually or after being admixed prior tobeing introduced into the reaction zone, which reaction zone should havea temperature of from about 150° C. to about 450° C.

The reaction zone preferably has a pressure of from 1 to 50 bar, morepreferably from 1 to 30 bar; a temperature of from about 150° C. toabout 450° C., more preferably from 200° C. to 300° C.; a contact timebetween the reaction mixture and the catalyst of from about 0.01 secondto 100 seconds, more preferably from 0.1 second to 10 seconds; and aspace hourly velocity of from about 50 to about 50,000 h⁻¹, morepreferably from 100 to 10,000 h⁻¹ and most preferably from 200 to 3,000h⁻¹.

The contact time is defined as the ratio between the apparent volume ofthe catalyst bed and the volume of the gaseous reaction mixture feed tothe catalyst bed under the given reaction conditions in a unit of time.

The space velocity is calculated by determining total reactor outlet gasequivalent, in liters, of the total effluent evolved over a period ofone hour divided by the liters of catalyst in the reactor. This roomtemperature volume is converted to the volume at 0° C. at 1 bar.

The reaction pressure is initially provided by the feed of the gaseousreactants and diluent and after the reaction has commenced, may bemaintained by the use of a suitable back-pressure controller placed onthe reactor outlet stream.

The reaction temperature may be provided by placing the catalyst bedwithin a tubular converter having walls placed in a circulating sandbath furnace heated to the desired reaction temperature.

The oxygen concentration in the feed gas mixture can vary widely, from0.1 to 50% or higher of the feed mixture by applying proper measures toavoid explosion problems. Air is the preferred source of oxygen in thefeed. The amount of oxygen present may be a stoichiometric amount, orlower, of the hydrocarbons in the feed.

The process is generally carried out in a single stage with all theoxygen and reactants being supplied as a single feed with non-reactedinitial reactants being recycled. However, multiple stage addition ofoxygen to the reactor with an intermediate hydrocarbon feed can also beused. This may improve productivity to acetic acid and avoid potentiallyhazardous conditions.

EXAMPLES

The following examples are illustrative of some of the products andmethods of making the same falling within the scope of the presentinvention. They are, of course, not to be considered in any waylimitative of the invention. Numerous changes and modifications can bemade with respect to the invention.

Several examples were carried out to demonstrate the invention using thetwo catalyst compositions given below.

Catalyst A

    Mo.sub.1 V.sub.0.396 Nb.sub.0.128 Pd.sub.3.84 E-04

Catalyst B

    Mo.sub.1 V.sub.0.628 Pd.sub.2.88 E-04 La.sub.1.0 E-05

Preparation Procedure for Catalyst A: Ammonium metavanadate (AldrichChemicals, Assay=99.0%) in the amount of 11.4 grams was added to 120 mlof distilled water and heated to 90° C. with stirring. 2.5 grams ofoxalic acid were added to obtain a clear yellow color solution with a pHbetween 5 and 6 (Solution A). 19.4 grams of niobium oxalate (21.5% Nb₂O₅, Niobium Products Company, USA) were added to 86 ml of water andheated to 65° C. with continuous stirring to give a clear white colorsolution with a pH of 1 (Solution B). Solution B was then combined withSolution A. The resultant solution was heated at 90° C. and 28 grams ofoxalic acid was added very slowly with continuous stirring to giveSolution C. Ammonium paramolybdate tetra hydrated (Aldrich ChemicalsA.C.S.--12054-85-2) in the amount of 43.2 grams was added to 45 ml ofwater and heated to 60° C. to give a colorless solution with a pHbetween 6.0 and 6.5 (Solution D). Solution D was combined slowly withSolution C to give dark blue to dark gray color precipitates (MixtureE). The required amount of palladium was added slowly to gel mixture.This dark color combination was stirred vigorously to achieve ahomogeneous gel mixture which was then dried slowly to incipient drynesswithin 60 to 120 minutes at 95-98° C. with continuous stirring.

The resulting solid was put in a China dish and dried additionally in anoven at 120° C. for sixteen hours. The dried material was cooled to roomtemperature and placed in a furnace. The temperature was raised fromroom temperature to 350° C. at the rate of 2°/min. and thereafter heldat 350° C. for four hours.

The calcined catalyst was formulated into uniform particles of the 40-60mesh size and evaluated for the ethane oxidative dehydrogenationreaction.

Preparation Procedure for Catalyst B: Ammonium metavanadate (AldrichChemicals, Assay=99.0%) in the amount of 6 grams was added to 65 ml ofdistilled water and heated to 90° C. with stirring. 6 grams of oxalicacid was added to the above solution. The color of the solution changesfrom yellowish green to dark brown with a pH 2-2.5 at 80° C. (SolutionA). Ammonium paramolybdate tetra hydrated (Aldrich ChemicalsA.C.S.--12054-85-2) in the amount of 14.4 grams was added to 16.7 ml ofwater and heated to 60-65° C. to give a colorless solution with a pHbetween 5.0 and 6.0 (Solution B). Solution A was mixed slowly withSolution B to give dark blue to dark gray color precipitates (MixtureE). The required amount of palladium followed by lanthanum nitrate wasadded slowly to gel mixture. This dark color combination was stirredvigorously to achieve a homogeneous gel mixture which was then driedslowly to incipient dryness within 60 to 120 minutes at 95-98° C. withcontinuous stirring.

The resulting solid was put in a China dish and dried additionally in anoven at 120° C. for sixteen hours. The dried material was cooled to roomtemperature and placed in a furnace. The temperature was raised fromroom temperature to 350° C. at the rate of 2°/min and thereafter held at350° C. for four hours.

The calcined catalyst was formulated into uniform particles of the 40-60mesh size and evaluated for the ethane oxidative dehydrogenationreaction.

For Examples 1 to 5, catalyst A was used, while for Examples 6 and 7,catalyst B was used.

The reaction products were analyzed on-line by gas chromatography.Oxygen, nitrogen and carbon monoxide were analyzed using a 2.5 m by 3 mmcolumn of 13× molecular sieve. Carbon dioxide and ethylene were analyzedusing a 0.5 m by 3 mm column packed with material sold under the tradename PORAPACK™ N. Acetic acid and water were analyzed using a 1.5 m by 3mm column packed with material sold under the trademark HAYASEP™ Q. Inall cases, the conversion and selectivity calculations were based on thestoichiometry:

    C.sub.2 H.sub.4 +O.sub.2 →C.sub.2 H.sub.4 O.sub.2

    C.sub.2 H.sub.4 +2O.sub.2 →2 CO+3 H.sub.2 O

    C.sub.2 H.sub.4 +3O.sub.2 +→2 CO.sub.2 +3 H.sub.2 O

The yield of acetic acid was calculated by multiplying the selectivityto acetic acid by ethylene conversion.

Example 1

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst A (40-60 mesh)and diluted with 3 g of silicon dioxide of the same mesh size. Thereactor was then heated to 285° C. in a sand bath thermostated furnaceand pressurized to 200 psi with nitrogen. A gas feed containing 14.79%ethylene and 85.21% air, by volume, was fed to the reactor at a flowrate of 58.30 cc/min. The liquid products were condensed in a cold trapand the gas products were analyzed on an on-line GC system.

Example 2

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst A (40-60 mesh)and diluted with 3 g of silicon dioxide of the same mesh size. Thereactor was then heated to 285° C. in a sand bath thermostat furnace andpressurized to 200 psi with nitrogen. A gas feed containing 14.94%ethylene and 85.06% air, by volume, was fed to the reactor at a flowrate of 60.40 cc/min. Water (8.85 cc/min. calculated as gas at STP) wasalso fed to the reactor inlet. The liquid products were condensed in acold trap and the gas products were analyzed on an on-line GC system.

Example 3

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst A (40-60 mesh)and diluted with 3 g of silicon dioxide of the same mesh size. Thereactor was then heated to 285° C. in a sand bath thermostat furnace andpressurized to 200 psi with nitrogen. A gas feed containing 15% ethyleneand 85% air, by volume, was fed to the reactor at a flow rate of 91.33cc/min. The liquid products were condensed in a cold trap and the gasproducts were analyzed on an on-line GC system.

Example 4

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst A (40-60 mesh)and diluted with 3 g of silicon dioxide of same mesh size. The reactorwas then heated to 285° C. in a sand bath thermostat furnace andpressurized to 200 psi with nitrogen. A gas feed containing 15% ethyleneand 85% air, by volume, was fed to the reactor at a flow rate of 90.60cc/min. Water (9.17 cc/min calculated as gas at STP) was also fed to thereactor inlet. The liquid products were condensed in a cold trap and thegas products were analyzed on an on-line GC system.

Example 5

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 7 g of calcined catalyst A (40-60 mesh)and diluted with 3 g of silicon dioxide of same mesh size. The reactorwas then heated to 240° C. in a sand bath thermostat furnace andpressurized to 250 psi with nitrogen. A gas feed containing 10.10ethylene and 89.9% air, by volume, was fed to the reactor at a flow rateof 35.33 cc/min. The liquid products were condensed in a cold trap andthe gas products were analyzed on an on-line GC system.

Example 6

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst B (40-60 mesh)and diluted with 3 g of silicon dioxide of the same mesh size. Thereactor was then heated to 285° C. in a sand bath thermostat furnace andpressurized to 200 psi with nitrogen. A gas feed containing 14.16%ethylene and 85.84% air, by volume, was fed to the reactor at a flowrate of 59.80 cc/min. Water (9.16 cc/min. calculated as gas at STP) wasalso fed to the reactor inlet. The liquid products were condensed in acold trap and the gas products were analyzed on an on-line GC system.

Example 7

A stainless steel tubular reactor measuring 0.760 cm (inside diameter)by 46 cm (long) was charged with 1 g of calcined catalyst B (40-60 mesh)and diluted with 3 g of silicon dioxide of the same mesh size. Thereactor was heated to 285° C. in a sand bath thermostat furnace andpressurized to 200 psi with nitrogen. A gas feed containing 14.31%ethylene and 85.69% air, by volume, was fed to the reactor at a flowrate of 59.90 cc/min. The liquid products were condensed in a cold trapand the gas products were analyzed on an on-line GC system.

The results of the tests with catalysts A & B under the reactionconditions described above are given in Table I and a typical analysisof the condensed product with impurities is given in Table II.

                                      TABLE I                                     __________________________________________________________________________    Ethylene Oxidation Data                                                                                       STY                                             Conversion (%) Selectivity (%) Yield (%) g.aa/l.cat/hr                      Example                                                                            Ethylene                                                                           Oxygen                                                                            Acetic acid                                                                         CO CO.sub.2                                                                         Acetic acid                                                                         Acetic acid                                   __________________________________________________________________________    1    62.87                                                                              97.68                                                                             61.07 3.72                                                                             34.45                                                                            38.5  635                                             2      77.33    98.25   77.82      0.96   19.83   60.18     1043                                             3      42.42    76.7    61.03      4.61                                       34.36   25.89     720                          4      63.42    81.8    78.03      1.75   20.15   30.57     1291                                             5      98.63    87.71   65.11      0.33                                       34.56   64.22      70                          6      86.14    98.44   80.00      1.40   18.60   68.9      1119                                             7      70.33    92.90   66.00      4.76                                       29.24   47        773                        __________________________________________________________________________     g.aa/l.cat/hr. = grams acetic acid per liter catalyst per hr.            

                  TABLE II                                                        ______________________________________                                        A Typical Analysis of Liquid Product.                                                          Component                                                                        wt %                                                      ______________________________________                                               Water    30.37                                                           Acetic acid             69.78                                                 Formaldehyde            0.118                                                 Methyl acetate          0.124                                                 Ethyl acetate           trace                                                 acetaldehyde            trace                                                 propionic acid          0.06                                                ______________________________________                                    

From the above-described results exhibited using the invention, thefollowing surprising and unexpected advantages may be derived:

1. High activity/conversion of ethylene reflects high rate of partialoxidation of alkene.

2. The invention provides a high rate of oxygenation of ethylene toacetic acid.

3. The invention provides a low rate of total oxidation to COx products.

4. The activity and selectivity to the oxygenation product, acetic acid,is increased while COx products are decreased with the addition of waterinto the feed and the magnitude of this impact depends on the amount ofwater used.

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

We claim:
 1. A single step process for the selective oxidation ofethylene to acetic acid comprising the step of contacting a reactionmixture containing ethylene with oxygen or a compound capable ofproviding oxygen in a reaction zone in the presence of a calcinedcatalyst represented by the formula Mo-V-Nb-Pd-O or Mo-V-La-Pd-O under areaction temperature sufficient to convert ethylene to acetic acid. 2.The process of claim 1, wherein said catalyst is in the form of a fixedor fluidized bed.
 3. The process of claim 1, wherein said mixturefurther comprises steam.
 4. The process of claim 1, wherein saidreaction mixture further comprises air.
 5. The process of claim 1,wherein said reaction mixture comprises oxygen.
 6. The process of claim1, wherein said mixture is a feed mixture introduced into said reactionzone.
 7. The process of claim 1, wherein said mixture comprisesmolecular oxygen ranging from 0.1 to 50% by volume of the feed mixture.8. The process of claim 1, wherein said mixture is diluted withwater/steam in an amount ranging from 0 to 50% by volume of the feedmixture.
 9. The process of claim 1, wherein said ethylene is in vaporform.
 10. The process of claim 1, wherein the reaction temperature isfrom 150 to 450° C.
 11. The process of claim 1, wherein said reactionzone under a pressure of from 1 to 50 bars.
 12. The process of claim 1,wherein said contacting provides a contact time between said reactionmixture and the catalyst of from 0.1 to 10 seconds.
 13. The process ofclaim 1, wherein said oxidation provides a 70% yield of acetic acid persingle pass through said reaction zone.
 14. The process of claim 1,wherein said oxidation provides a STY of 1400 (g. acetic acid/L. cat/hr)per single pass through said reaction zone.
 15. The process of claim 1,wherein said oxidation of ethylene produces less than 5 ppmacetaldehyde.
 16. The process of claim 1, wherein said mixture comprisesgreater than 10% by volume ethylene.
 17. The process of claim 1, furthercomprising the multistage of introduction of air or oxygen into thereaction zone to increase the yield, selectivity or combination of yieldand selectivity of acetic acid.
 18. A process for performing a catalyticchemical reaction in fluid phase comprising the step of contacting amixture containing at least one reactant in fluid phase with a calcinedcatalyst represented by the formula Mo-V-Nb-Pd-O or Mo-V-La-Pd-O undersuitable reaction conditions.
 19. The process of claim 18, wherein saidcatalytic chemical reaction converts one or more fluid phase reactantsto one or more fluid phase products.
 20. The process of claim 19,wherein said one or more fluid phase reactants comprise ethylene andsaid one or more fluid phase products comprise acetic acid.